Field of the Invention
The present invention relates to a diaphragm-actuated fluid control valve with a valve-driving diaphragm for controlling the flow rate or pressure of a fluid. In particular, the invention relates to a diaphragm-actuated fluid control valve which is suitable as an expansion valve used in the refrigeration cycle of air conditioners for vehicles and the like.
Background Art
As an example of an expansion valve used in the refrigeration cycle, there is known a diaphragm-actuated fluid control valve as disclosed in Reference 1 (JP Patent Publication (Kokai) No. 2007-240041 A). Specifically, this known control valve includes a valve for controlling the flow rate or pressure of a fluid (refrigerant), a valve body having an inlet port, an outlet port, and a valve opening (orifice) provided therebetween, which is adapted to be opened or closed by the valve, and a diaphragm device adapted to drive the valve in a direction to open or close the orifice.
In such a diaphragm-actuated fluid control valve, the diaphragm device typically has a diaphragm and a diaphragm-holding member that fixedly seals the outermost portion of the diaphragm in a manner sandwiching the outermost portion and defines a pressure chamber (also referred to as a “temperature-sensing chamber,” a “diaphragm chamber,” or the like) on the upper surface side of the diaphragm as a sealed space. In addition, an actuating rod is connected to the lower surface of the diaphragm so as to transmit the behavior (displacement) of the diaphragm to the valve.
One end of a capillary tube, for example, is inserted in the pressure chamber (the temperature-sensing chamber), and the other end of the capillary tube is provided with a thermo bulb (temperature sensing cylinder) which senses the temperature of refrigerant on the outlet side of an evaporator, for example. It should be noted that the interior of each of the temperature-sensing chamber, the capillary tube, and the thermo bulb is typically filled with a predetermined gas (e.g., carbon dioxide) with a predetermined pressure.
The diaphragm has a mountainous-wave portion formed between the outermost portion thereof, which is fixedly sealed by the diaphragm-holding member, and the innermost portion thereof on which a large-diameter disk portion abuts, the mountainous-wave portion having the shape of concentric circles when viewed in a plan view and having N elevated portions that protrude upward or downward when viewed in cross section, where N is a positive integer (1, 2, 3, . . . ).
In the diaphragm-actuated fluid control valve with the aforementioned structure, the diaphragm (the innermost portion of the diaphragm with respect to the outermost portion thereof) is typically displaced (flexes) in the up or down direction in accordance with the pressure difference between the pressure of the pressure chamber (the temperature-sensing chamber) (hereinafter referred to as “pressure on the upper surface side of the diaphragm”) and the pressure that acts on the lower surface of the diaphragm (hereinafter referred to as “pressure on the lower surface side of the diaphragm”). Such displacement is transmitted to the valve via the actuating rod, which in turn causes the valve to move in the orifice-opening or closing direction (the up or down direction) so that the valve opening degree (=the amount of lift=an effective opening area of the orifice) is controlled. Accordingly, the pressure (flow rate) of a fluid (refrigerant) flowing from the inlet port to the outlet port is controlled.